Catalysis of the ageing of alkali cellulose



Mgrh 15, 1960 B. LEoPoLD ETAL CATALYSIS OF THE AGEING OF ALKALICELLULOSE Filed Sept. 2, 1958 Hmoo e o m .Emoo e Qn ...moo e QN Hmoo .EEo. 5,58

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CATALYSIS OF THE AGEING F ALKALI CELLULOSE Bengt Leopold, Donald B.Mutton, and William R. Saxton, all of Hawkesbury, Ontario, Canada,assrgnors to Canadian International, Paper Company, Montreal, Quebec,Canada, a corporation of Canada Application September 2, l1958, SerialNo. 758,446

8 Claims. (Cl. 260-233) This invention relates broadly to thedepolymerization of cellulose. More particularly, the invention 1sconcerned with the catalytic ageing or depolymerization of .alkalicellulose obtained from various cellulosic materials such as wood,refined cotton, etc., to decrease its viscosity. The invention finds itsgreatest application 1n the viscose ture. The invention is also ofparticular value in ageing or depolymerizing alkali cellulose forproduction of cellophane, cellulose` ethers, or any other cellulosicproducts in the manufacture of which alkali cellulose is an intermediateproduct.

The manufacture of viscose rayon and cellophane employs solutions ofcellulose. In order to obtain solutions of low enough viscosity tohandle conveniently, the molecular weight of the cellulose must bereduced considerably from its original value in the wood, cotton orother cellulosic material from which it is obtained. This cellu- .losedepolymerization is carried out mainly in the case of wood during thecooking of the wood, the bleaching of the pulp, and the ageing of thealkali cellulose. Depolymerization by bleaching is expensive to thepulpvmanufacturer since it consumes large quantities of chemicals whichare not'inexpensive and it reduces yield. Ageing of alkali cellulose mayrequire a considerable'length of time and itis expensive and inefcientfor the rayon manumerization during ageingcould be increased suiciently,then all or rnost of the degradation now carried out during thebleaching and ageing steps could be performed -during the ageing periodalone, and even the ageingztime could be reduced. This would enable therayon manu- -facturer to save time and reduce costs and the pulp manu--facturer to reduce chemical costs as well as to sell higher viscositypulps which might yield improved rayon yarn of caustic soda as'asteeping liquid. To effect necessary .economy it is essential to reusethe caustic steeping solu- 4tions for treating subsequent batches ofpulp. When the -transition metal catalyst is relatively soluble in thesteepq ing alkali, variable amounts of the catalyst are retained by thesteeping liquid when separated from the alkali cellulose. This leads tolarge variations in ageing reactivity imparted to the `alkali cellulosesubsequently produced with the result that viscosity control is difcult.

This is especially true in the case of cobalt compounds which are muchmoreactive catalysts than compounds of manganese or iron. f

We have discovered that in accordance with the present If the rate ofdepoly-v 2,928,825 Patented Mar. 15,

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invention certain organic complexes or chelate com pounds of cobalt arenot lonly substantially completely insoluble in water and steepingcaustic, but what is more important and unexpected, these complexesretain the ability to catalyze the ageing of alkali cellulose. Thesealkali-insoluble complexes not only catalyze the ageing o'f alkalicellulose, but they are retained bythe alkali cellulose and do notcontaminate the steeping caustic. Consequently, the present inventionvmakes itv possible lto effectivelycatalyze the ageing of the alkalicellulosewithout contaminating the steeping caustic, thereby permitting.reuse of the steeping caustic without the concomitant variations inageing reactivity which have plaguedthe Vprior art. Since the steepingcaustic, after separation from the cellulose, contains substantially nocatalytic cobalt complex or chelate compound, it can be reused with thenext batch of cellulose to which an exact amount of catalyst has beenadded to produce controlled ageing'of the cellulose. During the researchinvestigation which resulted in the present invention it was found thatonly certain organic complexes or chelate compounds'of cobalt aresubstantially insoluble in steeping caustic and yet retain the abilityto catalyze the ageing or depolymerization of alkali cellulose.

lThe process of the invention provides greater control over the degreeof an rate of depolymerization. This control is important since too muchdepolymerization results in weakened rayon fiber strength.

It is an object of the present invention to provide improvements in thedepolymerization of cellulose.

It is also an object of the present invention to provide an improvedprocess for the controlled depolymerization of cellulose in themanufacture of viscose rayon and cellophane.

which are substantially insoluble in steeping alkali and yet catalyzethe ageing of alkali cellulose and which d0 not contaminate the steepingalkali.

The foregoing objects, as well as others,.wi1l be apparent to thoseskilled in the art from the present description, taken in conjunctionwith the accompanying coordinate diagram illustrating the effect ofvarying amounts of one of the cobalt complex catalysts on the ageing ofYalkali cellulose.

In accordance with the process of the present invention fordepolymerizing cellulose, a small amount of an alkaliinsoluble cobaltcomplex or coordinate compounds as hereinafter dened is brought into thepresence of cellulose, such as wood pulp, and steeping alkali tocatalyze cellulose depolymerization. Since such processes as the viscoseprocess and the manufacture of cellulose ethers involve conversion ofcellulose into alkali cellulose, usually by steeping sheets of cellulosein an equeous caustic soda solution containing from about 17 to 25% ofcaustic soda, it is desirable for use in that process to ,add the cobaltcomplex catalyst to the cellulose prior to the steeping operation. Afterthe cellulose has been steeped sufliciently in the alkali tosubstantially convert the cellulose to alkali cellulose, the alkalicellulose is separated from the steeping alkali by draining andpressing. The

'alkali cellulose, after comminution, is permitted t0 age essere@ cpbaltcomplex is sprayed or striped on to the formed pulp sheet as it passesinto the drier on the pulp machine or into the cutter. Alternatively,dilute solutions of .the cobalt complexes in an organic liquid, such aschloro` folim, may be employed. In accordance with another method, lthecobalt complex may be formed in situ on rthe cellulose by adding asoluble salt of cobalt, such as YAcobalt chloride, with, theinsolubilizing organic complexing agent, the latter being added inexcess of the ,stoichiometric amounts necessary to react with andcomplex substantially all the cobalt chloride.

Although any amount of cobalt complex catalyst may be added Yto thecellulose, it is usually necessary to add only very small amounts,because of the high catalytic activity of these complexes. In addition,we have found vthat increasing the amount of cobalt catalyst added tothe cellulose has progressively less effect on the rate of ageing, sothat normally there is little additional advantage in adding more thanp.p.m. of cobalt on the weight of bone dry cellulose. Similarly there isno lower limit to the amount of cobalt catalyst which may be applied tothe cellulose. We have found, however, that the ,lower the catalystconcentration, the more sensitive is the rate of ageing to smallvariations in the'catalyst concentration. For these reasons, we usuallyprefer to ern ploy between 0.5 and 3 p.p.m. of cobalt on the weight ofboue dry cellulose. As those skilled in the art will recognize, theoptimum amount of catalyst will vary .somewhat depending upon theoriginal pulp viscosity .andthe desired viscosity of the aged alkalicellulose, as well as time and temperature of ageing.

It is well known that cobalt forms coordinate compounds or complexeswith a wide variey of anions and neutral molecules. The essentialfeature of a coordinated group is that it contains an electron pairwhich it can share with the metal ion in the formation of a more or lesscovalent bond. Cobalt usually has a coordination nurnberof V6 and canthus form 6 essentially covalent -bondsvwith coordinated groups. In thecase of simple cobalt salts, ythe coordinated groups are usually watermolecules, 6 in number.

The cobalt complexes of the present invention are formed withbifunctional organic reagents which form more than one covalent bondwith the cobalt ion. When the positive charges of the cobalt `ion havebeen neutralized by coordinate groups, the Aresulting complex iselectrically neutral and is no longer Ian electrolyte. Thesecharacteristics of the cobalt complexes of the present invention areresponsible for their Ainsolubility in water and alkaline solutions.

The cobalt ion is capable of existing in the bivalent or trivalentstate. In its simple salts, such as the chloride, the cobalt is almostalways bivalent. Most complexes or coordinated compounds of cobaltusually occur with a trivalent cobalt ion. The cobalt complexes of thecpresent invention appear to occur -as mixtures of the complexes formedby bivalent and trivalent cobalt with the organic complexing agent.

While no precise valence can be ascribed to the cobalt in the complex,the complexes of the invention may be characterized in terms of theiralkali insolubility vand from the fact that they are produced byreacting a water-soluble salt or cobalt,

Ysuch as cobalt chloride, with a stoichiometric excess of the organiccomplexing agent.

the following structural formula:

wherein n is a number between 2 and3; "R is an'alkyl,

-cycloalkyl or aryl group.

VExamples of the cobalt complexes of the invention arethe complexes ofcobaltwith Qthy1xanthate, Vbutyl- `vxzmthatc, methylxanthate,cyclohexylxanthate and phenylxanthate.

In order more clearly to disclose the nature of the present invention,the following examples illustrating the invention are disclosed. Itshould be understood, however, that this is done solely by way ofexample and is intended neither todelineate the scope of the inventionnor limit the ambit of the appended claims. In the examples whichfollow, and throughout the specification, the quantities of materialsare expressed in terms of parts by weight, unless otherwise specified,and cobalt concentrations are expressed in terms of p.p.m. of cobalt perweight of bone-dry cellulose.

EXAMPLE 1 vthe cobalt complex suspension were 4required per square footof pulp. The pulp sheets were then air-dried in an atmosphere of 65%relative humidity. The dried pulp Y was steepedrfor 45 minutes at roomtemperature (22 C.) in the customary manner in a caustic soda steepingliquor containing 216.5 gms. of sodium hydroxide per liter of solutionAand containing also 5 gms. per liter of hemieellulose. The resultingalkali cellulose sheets were then drained and pressed to expel theVsteeping liquor to give a cellulose content of 32%. The sheets wereshredded and the alkali cellulose crumbs were aged for 24 hours at 22 C.Thecrumbs were then xanthated with 39% of carbon disulfide based on theweight of cellulose in the alkalicellulose by reacting for 21A hours at26 C. in the absence of air. The resultingxanthate was then mixed withdilute sodium hydroxide solution to give a viscose having a compositionof about 7% cellulose and 6% sodium hydroxide. The resulting viscose hada Vspinning viscosity of 26.1 seconds when measured by the falling ballmethod. A sample of identical pulp but without the ycobalt addition,processed in an analogous manner, required 65% .more ageing time to givethe same viscose spinning viscosity. The tensile and durabilityproperties of rayon produced from the viscose of the example and ofthecontrol were equivalent.

lcaustic by cobalt complex in the example was determined. The causticdrained and pressed from thepulp `was reused torsteep further batches ofcontrol pulp, su-

cient fresh .caustic being added to replace the caustic Control batchesof alkali cellulose employing the used caustic were ,-then aged and madeinto viscose as described and .the spinning viscosity/measured. It wasfound that, when caustic from Athe batch treated with cobalt complex wasreused, the .spinning viscosity of the second batch of .viscose wassubstantially the same as that obtained when caustic which had at notime been treated with cobalt -complex was used for steeping. vThisindicated that the Ycobalt complex catalyst was completely retained bythe -alkalicellulose and none of the complex contaminated the'recoveredsteeping caustic. On the other hand, when caustic usedto steep a batchof pulp containing the same amount of cobalt in the form of cobaltchloride was reused, the spinning viscosity of the viscose was less thanhalf that obtainedwhen caustic from the above example,employingthecobalt complex of the invention, was reused. This indicatedthe high degree of contamination of thersteeping caustic when employingan alkali-soluble cobaltsaln such as cobalt chloride.

EXAMPLE 2 `The foregoing example was repeated, except that varyweering'- amounts of cobalt ethylxanthate complex varying p.p.m. of cobalton pulp Time (hours) 0 0. 5 5. 0

EXAMPLE 3 The procedure of Example l was repeated employing the samewood pulp and alkali steeping liquor except that the 3 p.p.m. of cobaltwas provided by the cobalt phenylxanthate complex of Example 8herei-nbelow. When the catalyzed alkali cellulose crumbs were xanthatedand converted to viscose, it was found that the ageing time was reducedby 60%. When tested, the 'used steeping liquor was found to besubstantially free from cobalt contamination.

EXAMPLE4 The procedure of Example 1 was repeated employing the same woodpulp and alkali steeping liquor except that the 3 p.p.m. of cobalt wasprovided by the cobalt butylxanthate complex of Example 9. When thecatalyzed alkali cellulose crumbs were xanthated and converted toviscose, it was found that the ageing time was reduced by 75%. Whentested the used steeping liquor was found to be substantially free fromcobalt contamination.

EXAMPLE 5 The procedure of Example l was repeated employing the samewood pulp and alkali steeping liquor except that the 3 p.p.m. of cobaltWas provided by the cobalt methylxanthate complex of Example 10. Whenthe catalyzed alkali cellulose crumbs were xanthated and converted toviscose, it was found that the ageing time was reduced by 55%. Whentested, the used steeping liquor was found to be substantially free fromcobalt contamination.

EXAMPLE 6 The procedure of Example 1 was repeated employing the samewood pulp and alkali steeping liquor except that the 3 p.p.m. of cobaltwas provided by the cobalt cyclohexylxanthate complex of Example 11.When the catalyzed alkali cellulose crumbs were xanthated and convertedto viscose, it was found that the ageing time was reduced by 55%. Whentested, the used steeping liquor was found to be substantially free fromcobalt contamination.

The preparation of the alkali-insoluble cobalt organic complexesemployed in the foregoing examples is described in Examples 7-11 whichfollow:

EXAMPLE 7 COBALT ETHYLXANTHATE COMPLEX Pure potassium ethylxanthate(1.37 gm.), which is commercially available, was dissolved in 100 ml. ofwater EXAMPLE 8 COBALT PHENYLXANTHATE COMPLEX To a solution of 25 gm. ofphenol in 100 ml. of methyl alcohol were added 18 gm. of potassiumhydroxide. The mixture was refluxed for half an hour. Carbon disulphide(20 ml.) was added and refluxing was continued on the steam bath forfour hours. After standing overnight, the

mixture was filtered and cooled. Ether ml.) was added, and theprecipitated potassium phenyl xanthate was ltered off. The product'waswashed with ether and dried in the vacuum desiccator.

The substantially pure potassium phenyl xanthate (1.70 gm.) wasdissolved in 100 ml. of water and mixed with a solution of 1 gm. ofsodium carboxymethyl cellulose in 100 ml. of water. Tov this solutionwas added, with very vigorous stirring, a solution of 0.41 gm. of cobaltchloride hexahydrate in 50 ml. of water. (The molarratio of potassiumphenyl xanthate to cobalt was 5:1 in order to ensure complete reactionof the cobalt.) A very line g'reen suspension was formed of cobaltphenyl xanthate complex.

EXAMPLE 9 COBALT BUTYLXANTHATE COMPLEX A mixture of 100 gm. of n-butylalcohol and 18 gm. of potassium hydroxide pellets was reluxed for onehour and the residual solid was removed by decanting. Carbon disulphide(36 gm.) was added slowly and with constant shaking. The mixture wascooled in an ice bath and the potassium butylxanthate which separatedwas filtered ott and Washed with several 25 ml. portions of dry ether.The product was dried in a vacuum desiccator over silica gel.

The substantially pure potassium butylxanthate (1.61 gm.) was dissolvedin 100 ml. of water and mixed with a solution of 1 gm. of sodiumcarboxymethyl cellulose in 100 ml. of water. To this solution was added,with very vigorous stirring, a solution of 0.41 gm. of cobalt chloridehexahydrate in 50 ml. of water. (The molar ratio of potassiumbutylxanthate to cobalt was 5:1 in order to ensure complete reaction ofthe cobalt.) A very tine green suspension was formed of cobaltbutylxanthate complex.

EXAMPLE 10 COBALT METHYLXANTHATE COMPLEX Methyl alcohol (100 ml.) wasrefluxed with 25 gm. of potassium hydroxide pellets for 30 minutes andthe solution was decanted from any undissolved solid. Carbon disulphide(35 ml.) was added slowly with constant shaking. The mixture was cooledin an ice bath and the resulting crystals of potassium methylxanthatewere filtered oi and washed with dry ether. The product was dried in thevacuum desiccator.

The substantially pure potassium methylxanthate (1.25 gm.) was dissolvedin 100 ml. of water and mixed with a solution of 1 gm. of sodiumcarboxymethyl cellulose in 100 ml. of Water. To this solution was added,with very vigorous stirring, a solution of 0.41 gm. of cobalt chloridehexahydrate in 50 ml. of water. (The molar ratio of potassiummethylxanthate to cobalt was 5:1 in order to ensure complete reaction ofthe cobalt.) A very tine green suspension was formed of cobaltmethylxanthate complex.

7 EXAMPLE 1l COBALT CYCLOHEXYLXANTHATE COMPLEX l Cyclohexanol (100Y m13was refluxd with l8 of potassium hydroxide pellets for one hour and thesolution was cooled and lteredto remove any undissolved solid. Carbonrdisulphide (28.5 ml.) was added slowly with con-v stant shaking. Themixture was cooled in an ice Vbath and the resulting crystals ofpotassium cyclohexyl xanthate were filtered olf and washed with dryether. The product was dried in the vacuum desiccator.

The substantially pure potassium cyclohexyl xanthate (1.67 gm.) wasdissolved in 100 ml. of water and mixed with a solution of l gm. ofsodium carboxymethyl cellulose in 100V ml. of water. To this solutionwas added, with very vigorous stirring, a solution of 0.41 gm. of cobaltchloride hexahydrate in 50 ml. of water. (The molar ratio of potassiumcyclohex-yl xanthate to cobalt was 5:1 in order to ensure completereaction of the cobalt.) A very line green suspension was formed ofcobalt cyclohexyl xanthate complex. Y v

The terms and expressions which :have been employed are used as terms ofdescription and not of limitation, and there is no intention, in the useof such terms and expressions, of excluding any equivalents of thefeatures shown and described or portions thereof, but it is recognizedthat various modifications are possible within the scope of theinvention claimed.

What is claimed is:

1^. In the ageing of alkali cellulose the improvement which'comprisescatalyzing the ageing of the alkali cellulose with an alkali-insolublecobalt coordinate compound comprising a cobalt xanthate complex selectedfromV the class consisting of cobalt complexes of alkyl, cycloalkyl andaryl xanthates.

2. In the viscose process the improvement which com prises ageing thealkali cellulose in the presence of an alkaliiinsolble cobalt coordinatecompound comprising4 a cobalt'xanthate'complex selected from the classcon-1 sisting ofcobalt complexes of alkyl, cycloalkyl and arylXanthate's'. Y

3. In the `ageing of alkali cellulose, the improvement which comprisesageing alkali cellulose in the presence of an' organic cobalt complexhaving the following struc-V wherein n is a number between 2 and 3, R isa member selected from the class consisting of alkyl, cycloalkyl andaryl groups.

Y 4. Theimprovement in ageing alkali cellulose which comprises ageingl'the alkali cellulose in the presence of cobalt ethyl'xanthate complex.

5.` The improvement.

ageing alkali cellulose which'` comprises ageing the alkali cellulose inthe presence of References Cited in the tile of kthis patent UNITEDSTATES PATENTS 2,682,536 Mitchell .Tune 29, 1954 2,768,968 Reppe Oct.30, 1956A 2,841,579 Villefroy et al. July l, 1958

1. IN THE AGEING OF ALKALI CELLULOSE THE IMPROVEMENT WHICH COMPRISESCATALYZING THE AGEING OF THE ALKALI CELLULOSE WITH AN ALKALI-INSOLUBLECOBALT COORDINATE COMPOUND COMPRISING A COBALT XANTHATE COMPLEX SELECTEDFROM THE CLASS CONSISTING OF COBALT COMPLEXES OF ALKYL, CYCLOALKYL ANDARYL XANTHATES.